1. Field of the Invention
The invention relates to particular multi-layer structure and fabrication techniques for forming electrical devices, and in particular, for forming electrochromic devices of the sort used to modulate visible illumination.
2. Background Information
Generally speaking, an electrochromic device (‘ECD’) comprises two active layers separated by an electrolyte (sometimes referred to as an ‘EL’ or ‘EL layer’) through which a selected mobile ion can be controllably moved from one of the active layers to the other. Both of the active layers can contain varying concentrations of the mobile ion. In at least one of the active layers, commonly referred to as the ‘electrochromic layer’ (‘EC layer’), changes in the ion concentration are accompanied by changes in the color and transparency of the layer. In the other active layer, commonly referred to as the ‘ion storage layer’ (IS layer), changing the ion concentration may or may not be accompanied by notable changes in transparency or coloration. If the IS does not show a visible change, it is referred to as a “passive ion storage layer”. If the applied voltage causes an optical change in the IS layer similar to the one occurring in the EC layer, it is called a ‘complementary ion storage layer”.
Operation of an electrochromic device generally involves applying a DC voltage between the electrochromic and ion storage layers so as to cause the mobile ions to move from one layer to the other and to thereby selectively alter the coloration and transparency of the EC layer. This is commonly described in terms of the EC layer, or of the entire ECD, as being switched between ‘bleached’ and ‘colored’ states. Longstanding concerns of ECD development include finding film systems in which the transition between the two states is relatively speedy, can be accomplished with relatively low voltages, and provides a large change in transparency between the bleached and colored states. Another performance concern is maximizing the ‘self bleaching time’ of coloration decay after removal of the DC voltage.
In addition to the EC, EL, and IS layers, there are two electrode layers in an ECD, one abutting the EC layer and the other abutting the IS layer. The electronic conductivity of these layers is often an important consideration and can impose limitations on the switching speed and the uniformity of coloration.
Additional layers may be required in various ECD embodiments in order to protect the ECD during fabrication and service, or to prevent internal degradation. The most common additional external layer is an overcoat serving as an ambient moisture barrier. The overcoat layer is usually a transparent polymer that may be applied subsequent to vacuum processing by dipping, spraying, spinning, screening, or any other suitable approach.
In some ECDs additional layers (e.g., of silicon monoxide and silicon dioxide) are deposited between a flexible substrate and the EC electrode in order to provide improved adhesion and to prevent the otherwise brittle ECD from flaking off the substrate. It may be noted that avoiding the use of thick flexibility enhancing and adhesion promoting layers could reduce vacuum processing times.
Also, internal ion transfer layers are used in ECDs to enhance ion transport efficiency and to prevent degradation (e.g., oxidation) of earlier-deposited layers during either the deposition of subsequently formed layers or during processing steps at ambient pressure, as may be undertaken to provide metal bus bar contacts to the IS layer.